The discovery of rapamycin is such a fascinating story. Radiolab covered this a few years back - I encourage everyone to give it a listen: https://radiolab.org/podcast/dirty-drug-and-ice-cream-tub
The scientists looked in the soil samples
"Waaaaa why would you look in soil?? EWW!"
Anyway the compound stopped the fungus growing
"So it's sort of like it stopped time??"
Yes and it had a suppresive effect on the immune system
"So it's sort of like Elsa from Frozen it just freezes things??"
Yes, these are direct quotes from the episode, all within the first few minutes.